Re: emacs-24 r117050: Consult libpng-config more consistently.

[Darren Hoo <darren.hoo@gmail.com>]

I would like to remind  osx users that this change might cause build to
fail if HomeBrew (with libpng) or XQuartz is installed, unset PATH before
running ./configure so that libpng-config won't interfere.

A question about code around line 5919 of image.c,
Shouldn't this if conditional wrap the last line in?


	  /* We use the current frame background, ignoring any default
	     background color set by the image.  */
#if defined (HAVE_X_WINDOWS) || defined (HAVE_NTGUI)
	  XColor color;
	  png_color_16 frame_background;

	  color.pixel = FRAME_BACKGROUND_PIXEL (f);
	  x_query_color (f, &color);

	  memset (&frame_background, 0, sizeof frame_background);
	  frame_background.red = color.red >> shift;
	  frame_background.green = color.green >> shift;
	  frame_background.blue = color.blue >> shift;
#endif /* HAVE_X_WINDOWS */

	  fn_png_set_background (png_ptr, &frame_background,
				 PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);